We will test the hypothesis that: exercise training (EX) improves insulin (INS) sensitivity in type 2 diabetes (T2D), in part, by adaptations that improve skeletal muscle (skmus) blood flow (BF) via reversal of microvascular rarefaction and improved INS-induced endothelium-dependent dilation (EDD) of skmus arterioles. We propose that EX increases shear stress (Sw), decreases inflammation and blood glucose which work synergistically with INS in maintaining healthy endothelial (EC) phenotype and function in skmus arterioles. Preliminary results indicate that: 1) arteriolar EC's in T2D skmus are INS resistant leading to decreased INS-induced EDD, 2) that EX improves INS-EDD, and 3) that EX adaptations depend on skmus fiber recruitment patterns during sprint (IST) or aerobic (AEX) EX bouts. Two different EX protocols will be used, IST and AEX to test the hypothesis that IST has more beneficial effects due to greater adaptations in fast twitch skmus arterioles. Aim 1 will determine the distribution of decreased arteriolar INS- EDD, within and among T2D skmus, whether EX improves EDD in T2D skmus arterioles and determine whether EX and/or metformin treatment have positive interactions on EDD and INS receptor/second messenger signaling in EC of T2D skmus arterioles. Aim 2 will use microchip array, RT-PCR, immunoblot, and physiology techniques to explore 6 potential mechanisms for EX-induced improvement in EDD in arterioles of T2D skmus: 1) EX increases INS-EDD by altering expression of vascular genes in arterioles. 2) EX increases expression of enzymes that increase nitric oxide (NO) bioavailability, 3) EX decreases expression of markers/enzymes that decrease NO bioavailability (by generation of ROS and/or inflammation). 4) EX decreases vasoconstrictor responses. 5) EX improves INS-EDD by decreased ET-1 synthesis/release by EC., and 6) EX induces a healthy EC phenotype in all arteries. Aim 3 will explore the notion that interactions of Sw and INS can recapitulate effects of EX in modulation of arterial EC phenotype in T2D. We will determine whether INS and/or metformin work synergistically with Sw to induce a healthy EC phenotype in isolated skmus arterioles and whether Sw can restore a healthy EC phenotype in arterioles isolated from T2D skmus. Aim 4 examines microvascular rarefaction in T2D skmus (i.e. capillarity, arteriolar density and organization of the arteriolar tree), the relative importance of EX-induced changes in the capillary and arteriolar networks in reversal of microvascular rarefaction due to T2D and the role of NO in these phenomena. We propose that EX does not induce uniform improvement in endothelial function/phenotype in all arterial ECs but, instead, adaptations are focused in the arteries of skmus with the greatest relative increase in fiber activity during EX. This research, based on understanding of EX-induced adaptations in skmus arteriolar networks garnered over the past 25 years, will improve treatment of T2D through improved EX protocols plus drug treatment that will enhance EDD and glucose transport in T2D skmus.